In recent years, semiconductor devices such as an IC and LSI are highly integrated, and the semiconductor wafer micropatterning technique greatly advances along with this. Projection exposure apparatuses which play a central role in the micropatterning technique are an equal-magnification scanning exposure apparatus called a mirror projection aligner which exposes a mask and photosensitive substrate while scanning them by an equal-magnification mirror optical system having an arcuate exposure region, and a reduction projection exposure apparatus called a stepper which forms a mask pattern image onto a photosensitive substrate via a refraction optical system and exposes the photosensitive substrate by step & repeat.
Recently, a step & scan type scanning exposure apparatus which obtains high resolution and can increase the screen size is commercially available. An effective light source used in scanning exposure is a pulse light source, e.g., an excimer laser which emits pulses of short-wavelength light. To uniformly irradiate an irradiation surface with a pulse beam without any exposure nonuniformity while maintaining a uniform exposure amount on the irradiation surface in a scanning exposure apparatus using a pulse light source, it becomes important to properly set the pulse emission time and pulse emission interval of the pulse light source and their relationship with the irradiation surface moving velocity and the like.
In a conventional scanning exposure apparatus, no substrate is exposed in an acceleration section until the stage reaches a predetermined velocity from a still state in scanning and exposing a substrate, and a deceleration section until the stage reaches the still state from the predetermined velocity. In the conventional apparatus, the acceleration and deceleration sections do not contribute to exposure of a substrate, decreasing the throughput. Distances necessary for acceleration and deceleration must be ensured as a scanning range in addition to distances necessary for a reticle stage and wafer stage to pass through the illumination region. The moving ranges, i.e., moving strokes of the reticle stage and wafer stage become long. A prior art reference which gives attention to these problems is Japanese Patent Laid-Open No. 9-223662. In a scanning exposure apparatus disclosed in this reference, an emission control means causes a light source means to emit pulses at a frequency proportional to the moving velocity of the irradiation surface in irradiating the irradiation surface with a pulse beam from the light source means. Exposure is done even during acceleration/deceleration of the stage, thereby increasing the throughput.
In exposure even during acceleration, the sync error between the wafer stage and the reticle stage (i.e., a moving average (MA) and moving standard deviation (MSD) known as exposure precision indices) is large immediately after the start of acceleration. No substrate can be exposed at high precision.